1. Field of the Invention
The invention relates to a method for manufacturing a liquid crystal display (LCD) device, and more particularly, to a method for manufacturing a printing plate to realize a fine pattern.
2. Description of the Related Art
Various displays that can substitute for a cathode ray tube (CRT) have recently been developed, which have various advantages of portability, light weight, thin profile, small size, good picture quality, etc.
In general, an LCD device is includes a thin film transistor (TFT) array substrate, a color filter substrate, and a liquid crystal layer formed between the TFT array substrate and the color filter substrate. On the TFT array substrate, multiple gate lines are formed in perpendicular to multiple data lines, so as to define multiple pixel regions arranged in a matrix. Also, multiple TFTs are formed on unit pixel regions of the TFT array substrate, wherein the TFTs serve as switching devices. In addition, a pixel electrode of a transparent metal material is formed on the unit pixel regions. Then, RGB color filter layers and a black matrix layer are formed on the color filter substrate to correspond to the pixel electrode.
The TFT array substrate and the color filter substrate are separately manufactured. Before bonding the TFT array substrate and the color filter substrate to each other, steps of alignment coating, rubbing, spacer dispensing, and seal printing are sequentially performed.
After completing the above steps, the TFT array substrate and the color filter substrate are positioned opposite to each other, and then they are bonded to each other by heat and UV irradiation. At this time, a seal printing step is performed to bond the two substrates to each other and to prevent the outflow of liquid crystal molecules during injection of liquid crystals.
The seal printing step includes three methods or sub-steps of 1) a printing method, 2) a sandblasting method and 3) a dispensing method.
First, the printing method is generally used for manufacture of LCDs and plasma display panels (PDPs) because production facilities are simple and material efficiency is high. That is, after positioning a patterned screen above a substrate, a paste for formation of a wall is printed on the substrate by pressing. Through one printing process, it is possible to obtain a height of about 20 μm before firing. To form a wall having a height of 50 μm to 100 μm, it is necessary to perform the printing process 5 to 10 times, thereby requiring several drying steps. Accordingly, the printing method has low yield. In addition, since the glass substrate is deformed, it is difficult to realize high resolution.
Second, the sandblasting method is used to produce a fine wall of a large-sized panel. In the sandblasting method, a wall material is coated on a substrate, and is selectively removed to thereby form a wall. For example, a wall material is screen printed on an entire surface of a substrate. Then, a photoresist film is coated on the wall material and selectively patterned by exposure and development. After that, an abrasive material is sprayed onto the substrate so as to physically remove the substrate having no photoresist film, thereby forming the wall. At this time, the abrasive material may be used of Al2O3, SiC or glass particles, which is sprayed using compressed air or nitrogen gas. By the sandblasting method, it is possible to form the wall of 70 μm or less on the large-sized substrate. However, the glass substrate may be broken due to physical impact during firing. Also, the process of sandblasting is complicated, whereby the manufacturing cost increases. Further, an environmental pollution may be generated due to dust.
Third, the dispensing method is generally used for sealing a large-sized LCD or PDP. In the dispensing method, a paste is directly dispensed on a substrate by air pressure using line data from computer-assisted design (CAD) used for manufacture of a mask. In the dispensing method, it is possible to reduce the manufacturing cost of the mask, to obtain great degree of freedom for formation of a thick film, and to realize the simplified process and various applications.
FIG. 1 shows a schematic view illustrating a printing apparatus according to the related art. As shown in FIG. 1, the related art printing apparatus includes a printing table 11 supporting a substrate 10, a printing plate 1 having a convex (or concave) pattern 2 (for printing a pattern 4 on the substrate 10), a plate body 12, an anilox roll 16, a dispenser 18, and a doctor roll 15.
Then, a printing material 17 (for example ink) is supplied to the anilox roll 16 by the dispenser 18. The anilox roll 16 and the plate body 12 are formed in shape of cylindrical roll. The anilox roll 16 and the plate body 12 respectively revolve in arrow directions 48 and 46 and are in contact with each other.
The printing plate 1 adheres on an outer surface of the plate body 12, wherein the printing plate 1 has the convex (or concave) pattern 2 having a desired shape. The convex pattern 2 is positioned to be in contact with the substrate 10.
Also, the printing material 17 is supplied from the anilox roll 16 to the convex pattern 2, and then the printing material 17 of the convex pattern 2 is printed on the substrate 10. The substrate 10 is positioned on the printing table 11. During printing, the substrate 10 is moved to an arrow direction 47.
The printing material 17 printed on the substrate 10 has a shape or pattern 4 corresponding to the convex pattern 2, which is referred to as the printing result. Here, the printing result is formed in shape of frame.
The anilox roll 16 is in contact with the doctor roll 15 as well as the convex pattern 2. The doctor roll 15 uniformly coats the printing material 17 supplied from the dispenser 18 onto the outer surface of the anilox roll 16. Accordingly, the doctor roll 15 is in contact with the anilox roll 16 within a range between a portion of supplying the printing material 17 and a portion being in contact with the convex pattern 2. Instead of the doctor roll 15, a plate-shaped doctor blade may be used. Also, instead of the dispenser 18, another cylindrical roll may be used so as to provide the printing material 17 to the anilox roll 16.
Generally, the printing apparatus is used to form letters or figures on packing paper. However, the printing apparatus may be used to form various patterns on thin films. For example, an alignment layer or a sealant may be printed on a glass substrate of an LCD device by printing a polyimide thin film.
Hereinafter, a method for manufacturing a printing plate according to the related art will be described with reference to the accompanying drawings.
FIGS. 2A to 2E are cross sectional views illustrating a related art method for manufacturing a printing plate.
As shown in FIG. 2A, a metal layer 52 for a hard mask is deposited on an insulating substrate 51, and photoresist 53 is coated on the metal layer 52. The metal layer 52 is formed of Cr or Mo. Then, the photoresist 53 is selectively patterned by exposure and development to thereby define a pattern area.
Referring to FIG. 2B, the metal layer 52 is selectively removed using the patterned photoresist 53 as a mask to thereby form a metal layer pattern 52a. 
As shown in FIG. 2C, the photoresist 53 is removed. The photoresist 53 is removed using oxygen gas plasma or various oxidizers to form the metal layer pattern 52a. When using oxygen gas plasma, oxygen gas plasma is generated by providing oxygen gas under vacuum and high voltage conditions, and the oxygen gas plasma decomposes the photoresist, whereby the photoresist is removed.
As shown in FIG. 2D, the exposed insulating substrate 51 is selectively etched using the metal layer pattern 52a as a mask to thereby form a trench 54 having a depth of about 20 μm. When etching the insulating substrate 51, an isotropic etching method using HF-based etchant is used.
As shown in FIG. 2E, the metal layer pattern 52a is removed, thereby completing the printing plate.
The completed printing plate is then installed on the printing apparatus shown in FIG. 1. Then, after the printing material is coated on the anilox roll, the anilox roll is in contact with the printing plate. Thus, the printing material is printed on the predetermined pattern of the printing plate, and the printing material of the printing plate is printed on the substrate to thereby obtain the printing result of the predetermined pattern.
However, the related art method for manufacturing the printing plate has the following disadvantages.
In the method for manufacturing the printing plate according to the related art, the trench having the predetermined depth is formed by the isotropic etching method of etching the insulating substrate using the metal layer pattern as the mask, whereby the etching critical dimension (CD) is large. As a result, it is difficult to manufacture a precise printing plate. That is, if the etching thickness of the insulating substrate is about 5 μm, it is impossible to obtain a line width of 10 μm or less (‘A’ of FIG. 2D).